Posterolateral fusion is the standard procedure for treating high grade spinal disorders such as spinal stenosis as well as spondylolisthesis. Despite the wide-spread use of posterolateral fusion as a surgical approach for correcting back pain, numerous problems have been associated with its use. Spinal fusion recipients may be at risk for developing Adjacent Segment Disease (ASD), a condition in which the motion segments adjacent to the fused vertebral segments experience higher rates of degeneration deterioration due to an increase in vertebral loading, higher intradiscal pressures, increased range of motion, and increased facet motion.
Dynamic spinal stabilization has recently emerged as an alternative procedure to treat many degenerative spinal disorders. Existing dynamic stabilization devices restore stability to an injured spine while simultaneously allowing a restricted range of motion. These devices are designed to preserve the integrity of adjacent segments by minimizing the transfer of segment motion and facet joint forces between the stabilized spinal segment and the adjacent spinal segments.
Existing dynamic spine stabilization devices incorporate selectively flexible elements such as flexible cords and intravertebral spacers, or flexible spring rods in order to allow a constrained range of motion to the stabilized spinal segment. To date, no existing dynamic spine stabilization device constrains the rotation of the stabilized segments to a center of rotation that is coincident with a physiological center of rotation. Physiologically representative loading of a spinal segment that is stabilized using a dynamic stabilization device is unlikely to occur unless the rotational motion of the spinal segment passes through the spine's natural center of rotation. The imposition of a non-physiological center of rotation location by existing dynamic stabilization devices may result in alterations to the physiological pattern of tissue stresses and may further increase the likelihood of hardware failure. These altered tissue stresses and non-physiological motion patterns may also be induced in adjacent motion segments, increasing the likelihood of long-term complications, such as ASD, associated with existing stabilization procedures.
There is a need in the art for a dynamic spinal stabilization system that not only allows limited motion of injured or deteriorated vertebral segments, but that constrains that motion to a range that is consistent with the range of motion of the corresponding normal healthy vertebrae. In particular, a need exists for an existing dynamic spine stabilization system in which the vertebrae are constrained to rotate about an axis that is consistent with a normal healthy spine.